<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <script>
      let obj = {
        id: 1,
        name: 'andy',
        msg: {
          age: 18
        }
      }
      let o = {}
      o = JSON.parse(JSON.stringify(obj))
      console.log('o', o)
      o.msg.age = 20
      console.log({ o, obj })
    </script>
  </body>
</html>

